Cathode Material For Sodium-ion Batteries Research Articles

Hydrogen Sodium Vanadium Oxide Hydrate with Oxygen Vacancy: A New Layered Cathode Material for Sodium-Ion Battery

Hydrogen Sodium Vanadium Oxide Hydrate with Oxygen Vacancy: A New Layered Cathode Material for Sodium-Ion Battery

Optimizing Dopant for Enhanced Oxygen-Redox Performance in P2-Na Cathode Materials for Sodium-Ion Batteries

Recently, there has been a lot of interest in using oxygen-redox-based cathode materials for sodium-ion batteries (SIBs) due to their potential for providing additional capacity in the high-voltage range. However, they have some matter, including fast capacity fading and poor rate capability. Herein, P2-Na0.7[Li0.1Ni0.1Mg0.1Mn0.7]O2 is introduced, an layered oxide cathode material for Na-ion batteries based on oxygen-redox. The effect of Ni doping is improved electrochemical performance. Mg2+ in transition metal layer delivered relatively higher capacity via oxygen redox in high voltage region by comparison with Mg-free P2-Na0.75[Li0.15Ni0.15Mn0.7]O2, showing a specific discharge capacity of 175mAh g-1 with 83% of capacity retention after 100 cycles. This study show how the co-doping of Li, Ni and Mg can impact P2-type layered materials and proposes a novel approach to utilizing Mn-rich cathode materials through oxygen redox, with a focus on optimizing the dopant for sodium-ion batteries.

Enhancing Structural of P2-Type Layered Cathode Material for Sodium-Ion Batteries through Cu Substitution

Oxygen-redox-based layered cathode materials for Sodium-ion batteries (SIBs) have been recognized as a promising alternative to Lithium-ion batteries (LIBs) due to high energy density and additional capacity in the high voltage. However, their irreversible oxygen-redox activity during cycling leads to structural distortion and capacity fading. Herein, we introduce a layered P2-Na0.75[Li0.15Cu0.15Mn0.7]O2 cathode material, in which Cu substitution improves electro-conductivity and cyclability. Na0.75[Li0.15Cu0.15Mn0.7]O2 delivers a reversible capacity of 170 mAh g-1 at 0.1C in Na cell. Operando-XRD measurement display the material maintain the P2 structure even upon full Na+ extraction and insertion. Furthermore, magnetic susceptibility provide further information Cu2+/Cu3+, Mn3+/Mn4+, and O2-/(O2)n- ion distribution in Na0.75[Li0.15Cu0.15Mn0.7]O2. This research highlight the effect of Li and Cu doping in P2-type layered materials and the contribution of oxygen redox to additional capacity in high voltages, suggesting the potential for future development of cathode materials for Na-ion batteries with oxygen redox.

Increasing the Sodium Content in P2-Type Layered Oxides As Cathode Materials for Sodium-Ion Batteries

P2-type layered oxides exhibit superior Na ion conductivity and structural stability compared to their O3 analogues, making them promising candidate materials for next generation batteries. However, their lower initial Na contents (Na/transition metals < 1) restrict their capacity during the first charge process, and the transitions between P- and O2-type structures during cycling further deteriorate their stability.[1,2] Our work aims to increase the Na inventory in pristine cathode compositions, especially relevant for full cell systems, while maintaining their cycling stability. We started with the well-studied P2 material Na2/3Ni1/3Mn2/3O2 and have worked on incorporating Li in the transition metal layers to stabilize the structure, while at the same time increasing the Na content.[3,4] In this respect, a great challenge is to control the phase formation during the synthesis. When the Na content exceeds a certain limit, an O3 structure is more likely to form than a P2 structure.[1] On the other hand, at too low temperatures, a P3 polymorph is preferred.[5] By regulating the synthesis conditions, Na contents have been successfully increased in a series of materials between two end compositions, Na2/3Ni1/3Mn2/3O2 and Na5/6Li5/18Mn13/18O2.In this presentation, we report on unpublished in situ XRD characterizationsof these compositions during their solid-state synthesis, as well as on their crystal structures and electrochemical behavior, which involves varying amount of Ni redox. These time-resolved studies of structural evolutions provide guidance for further synthesis of desired phases and compositions. Along with the electrochemical results, we also aim to answer the questions on the charge compensation mechanisms that sustain the electrochemical performance as the amount of Li increases and Ni decreases. Finally, we also explore which amount of Li substitution can best balance the structural stability and capacity retention of the cathode material.

Mn-Rich P′2-Na0.67[Ni0.1Fe0.1Mn0.8]O2 As High-Energy-Densityand Long-Life Cathode Material for Sodium-Ion Batteries

P′2-type Na0.67[Ni0.1Fe0.1Mn0.8]O2 is introduced as a promising new cathode material for sodium-ion batteries (SIBs) that exhibits remarkable structural stability during repetitive Na+ de/intercalation. The O-Ni-O-Mn-O-Fe-O bond in the octahedra of transition-metal layers is used to suppress the elongation of the Mn-O bond and to improve the electrochemical activity, leading to the highly reversible Na storage mechanism. A high discharge capacity of ≈220 mAh g−1 (≈605 Wh kg−1) is delivered at 0.05 C (13 mAg−1) with a high reversible capacity of ≈140 mAh g−1 at 3 C and excellent capacity retention of 80% over 200 cycles. This performance is associated with the reversible P′2–OP4 phase transition and small volume change upon charge and discharge (≈3%). The nature of the sodium storage mechanism in a full cell paired with a hard carbon anode reveals an unexpectedly high energy density of ≈542 Wh kg−1 at 0.2 C and good capacity retention of ≈81% for 500 cycles at 1 C (260 mAg−1).

Advances in 2D Ultrathin Nanosheets of a2FeSiO4 (A= Li, Na, K) for Next-Generation Alkali-Ion Batteries

Although lithium-ion batteries (LIBs) have become ubiquitous in various applications, the limited resource of Li and increasing cost hinder their scalability for grid-scale energy storage applications. Thus, alternative rechargeable batteries that use more earth-abundant elements such as sodium and potassium have received significant attention. However, the distinct different properties of Li+, Na+, and K+ ions hinder the extensive development of universal host materials for alkali metal ions. Polyanion-type electrode materials, which contain polyanionic groups (XO4)n −, (XO4F)n −, and (XmO2m+1)n − (X = P, Si, S, etc.), have garnered significant interest owing to their remarkable structural stability and adjustable electrode potential; this properties make them excellent candidates as cathode materials in sodium-ion batteries (SIBs) and potassium-ion batteries (KIBs). Among these, A2FeSiO4 (AFS) (A= Li, Na, K) is highlighted as a promising cathode material due to its abundant Fe resources, low cost, and non-toxicity. The crystal structure, transport pathways, and synthesis techniques of Li2FeSiO4 (LFS) have been extensively explored whereas research on Na2FeSiO4 (NFS) as a cathode material is still in the process of maturing and research on K2FeSiO4 (KFS) is very rare. The large ionic radius of sodium and potassium presents a significant challenge to effective ion-intercalation reactions for energy storage in electrodes, destabilizing the crystal structures of host materials. In addition, orthosilicates exhibit poor electronic conductivity, greatly limiting its practical application. To address this issue, various techniques have been explored, which include nanostructuring, coating with conductive polymers, and metal doping. In this study, a facile solvothermal technique for the fabrication of ultrathin 2D AFS nanosheets by hydrothermal transformation and propose the reaction mechanism for this chemical transformation. The as-obtained AFS nanosheets are highly exfoliated using oxalic acid as the exfoliating agent to improve their electrochemical performance. These nanosheets are designed to mitigate the diffusion limitations encountered by alkali ions when traversing the densely packed structure of AFS. The highly exfoliated AFS 2D nanosheets greatly improve the electrochemical performance and cyclability of the cathode. The nanosheets exhibit a specific discharge capacity of 149 mAh g-1 for Li+, 99 mAh g-1 for Na+, and 88 mAh g-1 for K+ when operated at a current density of 100 mA g-1. Moreover, the nanosheets display exceptional capacity retention, with a retention rate of 75% for Li+, 99% for Na+, and 65% for K+ after 100 charge/discharge cycles for each of the cathodes. This study demonstrates the potential of 2D nanosheets for stabilizing the silicate-based cathode materials against structural and volume changes, and for improving their electrochemical performance in SIBs and KIBs. Figure 1

Electrochemical Strategies to Control Dendritic Growth in Sodium-Metal Batteries

Sustainable development can be pursued through electrification in all sectors, and energy storage devices -mainly batteries- play a crucial role in this process. This leads to an ever-increasing demand for rechargeable batteries. However, the current generation of the rechargeable batteries, namely lithium-ion batteries, is produced using elements such as Li, Ni, and Co which have limited resources. Sodium-ion batteries (SIBs) on the other hand are considered as a good alternative due to the abundance of Na resources and fundamental similarities of Na and Li. While the cathode material for SIBs has reached a commercial level of reliability, the identification of a high energy anode material still remains a challenge. Although Na metal as an anode material offers high energy density, the main issue is that Na metal has a tendency for dendritic growth during electrodeposition.In this work, different electrochemical strategies are used to mitigate dendritic Na growth. High overpotential nucleation pulses during stripping and/or plating steps are applied in order to induce two-dimensional growth. The impact of these strategies is studied using three-electrode symmetrical cells with Na metal as the working, counter, and reference electrodes, in an electrolyte composed of NaPF6 in EC/PC with FEC as an additive. Chronopotentiograms recorded during extended cycling (with and without Na pre-nucleation) are examined with special attention being paid to the overpotentials occurring on each cycle. Ex-situ SEM images are used to relate the different potential profiles during extended galvanostatic cycling to the different surface morphologies.The results show that a combination of oxidative (stripping) and reductive (plating) pulses has an obvious effect on inhibiting dendritic growth during electrodeposition of Na metal. The results encourage the deployment of electrochemical strategies to prevent dendritic growth in Na metal anodes and paves the way for experiments with new electrolyte compositions to further help overcoming the challenges associated with Na deposition.

Engineering Transition Metal Layers for Long Lasting Anionic Redox in Layered Sodium Manganese Oxide

Oxygen-redox-based layered cathode materials are of great importance in realizing high-energy-density sodium-ion batteries (SIBs) that can satisfy the demands of next-generation energy storage technologies. However, Mn-based layered materials (P2-type Na-poor Nay[AxMn1−x]O2, where A=alkali ions) still suffer from poor reversibility during oxygen-redox reactions and low conductivity. Herein, we introduce P2-Na0.75[Li0.15Ni0.15Mn0.7]O2 and P2-Na0.6[Li0.15Co0.15Mn0.7]O2, an oxygen-redox-based layered oxide cathode materials for SIBs. The effect of Ni and Co doping on the electrochemical performance was investigated by comparison with Ni-free and Co-free P2-Na0.67[Li0.22Mn0.78]O2 material. Combined experiments (galvanostatic cycling, neutron powder diffraction (NPD), X-ray absorption spectroscopy (XANES), X-ray photoelectron spectroscopy (XPS), and nuclear magnetic resonance (7Li NMR)) and theoretical studies (density functional theory, DFT calculations) confirmed that Ni substitution not only increases the operating voltage and decreases voltage hysteresis but also improves the cycling stability by reducing Li migration from transition metal (TM) to Na layers. It is also anticipated that having Na–O–Li configuration in a Mn4+-based layered material is important to active oxygen redox and that Co doping is crucial for improving the electrical conductivity. This research demonstrates the effect of Ni and Co doping in P2-type layered materials and suggests a new strategy of using Mn-rich cathode materials via oxygen redox with optimization of doping elements for SIBs.

Preparation and Electrochemical Performance of Na2-xLixFePO4F/C Composite Cathode Materials with Different Lithium/Sodium Ratios.

With their advantages of abundant raw material reserves, safety, and low toxicity and cost, sodium-ion batteries (SIBs) have gained increasing attention in recent years. Thanks to a high theoretical specific capacity (124 mAh g-1), a high operating voltage (about 3.2 V), and a very stable three-dimensional layered structure, sodium ferric fluorophosphate (Na2FePO4F, NFPF) has emerged as a strong candidate to be used as a cathode material for SIBs. However, applications are currently limited due to the low electronic conductivity and slow ion diffusion rate of NFPF, which result in a low actual specific capacity and a high rate performance. In this study, the authors used a high-temperature solid-phase technique to produce Na2-xLixFePO4F/C (0 ≤ x ≤ 2) and evaluated the impact on electrode performance of materials with different Na+ and Li+ contents (values of x). Transmission electron microscopy (TEM) and X-ray diffraction (XRD) were also used to analyze the material's crystal structure and nanostructure. The results show that the material had the best room-temperature performance when x = 0.5. At a charge-discharge rate of 0.1 C, the first discharge-specific capacity of the resulting Na1.5Li0.5FePO4F/C cathode material was 122.9 mAh g-1 (the theoretical capacity was 124 mAh g-1), and after 100 cycles, it remained at 118 mAh g-1, representing a capacity retention rate of 96.2% and a Coulomb efficiency of 98%. The findings of this study demonstrate that combining lithium and sodium ions improves the electrochemical performance of electrode materials.

A Ni/Co-free high-entropy layered cathode with suppressed phase transition and near-zero strain for high-voltage sodium-ion batteries

High-entropy layered oxides have emerged as a new class of cathode materials for sodium-ion batteries by providing infinite possibilities to tailor energy storage capabilities. However, owing to the lack of advanced high-entropy layered material, the influence of configurational entropy/compositional disorder on the high-voltage electrochemical performance of sodium-based layered cathode has seldom been explored. In this work, a Ni/Co-free high-entropy layered oxide P2-Na0.65Mn0.65Cu0.2Li0.06Mg0.015Ti0.015Al0.015Zr0.015Y0.015La0.015O2 (Mn-Cu-HEO) was prepared by stirring hydrothermal method, and investigated as a new cathode material for sodium-ion batteries. It is found that high configurational entropy and strong M−O configurations (M = Ti, Al, Zr, Y, and La) greatly stabilize the layered framework structure and MnO6 octahedral local structure, restraining the deleterious phase transition and large volume change during high-voltage cycling, thus resulting in high reversible cationic/anionic redox. In the meantime, disordered atomic arrangement in transition metal layer efficaciously mitigates Na+/vacancy ordering during de-/sodiation, enhancing the Na+ transport kinetics. Benefiting from the high-entropy stabilization effect, complex atomic arrangement, and multielemental composition, Mn-Cu-HEO displays splendid cyclic stability (87.2 % capacity retention after 500 cycles, very small change in cell volume (0.53 %) after 100 cycles), excellent rate capability (55.5 mAh g−1 at 10C), and a usable reversible capacity of 85.1 mAh g−1 at 1C in high-voltage range of 2.0–4.5 V. This work expands the horizons of high-entropy layered materials, providing new insight in the design and construction of highly stable and high-voltage sodium ion host.

Enhanced Electrochemical Performance of Ca-Doped Na3V2(PO4)2F3/C Cathode Materials for Sodium-Ion Batteries.

Na3V2(PO4)2F3 (NVPF) with a NASICON structure has garnered attention as a cathode material owing to its stable 3D structure, rapid ion diffusion channels, high operating voltage, and impressive cycling stability. Nevertheless, the low intrinsic electronic conductivity of the material leading to a poor rate capability presents a significant challenge for practical application. Herein, we develop a series of Ca-doped NVPF/C cathode materials with various Ca2+ doping levels using a simple sol-gel and carbon thermal reduction approach. X-ray diffraction analysis confirmed that the inclusion of Ca2+ does not alter the crystal structure of the parent material but instead expands the lattice spacing. Density functional theory calculations depict that substituting Ca2+ ions at the V3+ site reduces the band gap, leading to increased electronic conductivity. This substitution also enhanced the structural stability, preventing lattice distortion during the charge/discharge cycles. Furthermore, the presence of the Ca2+ ion introduces two localized states within the band gap, resulting in enhanced electrochemical performance compared to that of Mg-doped NVPF/C. The optimal NVPF-Ca-0.05/C cathode exhibits superior specific capacities of 124 and 86 mAh g-1 at 0.1 and 10 C, respectively. Additionally, the NVPF-Ca-0.05/C demonstrates satisfactory capacity retention of 70% after 1000 charge/discharge cycles at 10 C. These remarkable results can be attributed to the optimized particle size, excellent structural stability, and enhanced ionic and electronic conductivity induced by the Ca doping. Our findings provide valuable insight into the development of cathode material with desirable electrochemical properties.

Off-stoichiometric NaxV2(PO4)3 as cathode material for sodium-ion batteries

The NASICON-type compound Na3V2(PO4)3 (NVP) has garnered significant attention as a promising cathode material for sodium-ion batteries. However, the practical application of the NVP cathode still face challenges due to its intrinsic limitation of electronic conductivity and cycling stability. Herein, a novel off-stoichiometric NaxV2(PO4)3 cathode is synthesized, and the effects of compositional variations on both structural stability and electrochemical properties are investigated. Particularly, the optimized Na3.3V2(PO4)3 electrode exhibits superior cycling stability with a capacity retention of 86.7 % after 400 cycles, and excellent rate capability, achieving a capacity of 90 mAh g−1 at 5 C. Through a combination of electrochemical analysis and first-principle calculations, it is elucidated that the excess Na+ content within the structure effectively expands lattice volume, thereby mitigating migration barriers for enhanced ion diffusivity.

Trace Ti/Mg co-doped O3-type layered oxide cathodes with enhanced kinetics and stability for sodium-ion batteries

O3-type layered oxide cathodes are identified as a promising cathode material for sodium-ion batteries (SIBs) due to their high specific capacity and moderate operating voltage, yet it usually suffers from sluggish Na-ion diffusion and structure instability. Herein, we demonstrate the synthesis of a trace Ti/Mg co-doped NaNi1/3Fe1/3Mn1/3O2 (TiMg-NFM) cathode, in which Ti-ion is distributed in transition metal layers and Mg-ion is doped into sodium layers. The co-doping can enlarge the Na-layer spacing inside the layered structure to reduce Na-ion diffusion barrier. Meanwhile, the structural stability is effectively reinforced via the stronger Ti-O bond and the pillar effect of Mg-ions, further reducing surface side reaction with electrolyte. These merits endow a high reversible capacity of the TiMg-NFM cathode with 144.5 mAh g−1 at 0.1C, and much higher capacity retention of 111.4 mAh g−1 at 5C versus the pristine NFM (62.1 mAh g−1). More impressively, 80.1% of initial capacity can be maintained after 300 cycles at 2C. This work presents a feasible strategy to enhance the reaction kinetics and structure stability for developing advanced O3-type layered oxide cathodes.

Improved rate capability and long cycle life of metal-organic framework derived TiO2@V2O5 composite as an efficient cathode for sodium-ion batteries

Vanadium oxide on carbon nanoporous structure (V2O5/C) as a potential cathode material for sodium-ion batteries (SIBs) offers significant specific capacities in energy storage systems but suffers from slow ionic diffusivity upon long cycling at higher current rates, thereby generally resulting in substandard electrochemical performance. This study suggests a facile strategy to enhance the electrochemical performance of V2O5/C as a cathode in sodium-ion batteries via titanium (Ti) doping using the pre-synthesized Ti-doped vanadium-based metal-organic framework template (V-MIL-101) as the precursor, which can be converted into a sophisticated core-shell type structure in which titania nanoparticle-based shell surrounds the vanadium oxide with a porous carbon-based octahedral core. Structural characterization reveals that Ti-doping forms a protective layer around vanadium based MIL-101 octahedrons that, upon pyrolysis, preserves the octahedral geometry and transforms into a nanoporous core-shell structure. It also greatly enhances the electrochemical performance as a cathode for SIBs. The titania-doped vanadium oxide structures represent higher specific capacities than the undoped vanadium oxide cathode, whereas among all the titania-doped samples, the 3 wt% TiO2@V2O5/C exhibited a much higher reversible capacity of 276.2 mAh/g as compared to the other cathode samples at 0.1C current rate and was able to retain a capacity of 250.1 mAh/g with a high coulombic efficiency after 200 cycles. Titanium species induce the formation of oxygen vacancies and V+5 species, which enhance the electrode's electric conductivity and ion diffusion—the stable octahedrons with a porous structure and carbon hybridisation in 3 wt% TiO2@V2O5/C could facilitate ion/electron transfer through shortened diffusion pathways.

First-principles study on the properties of Ta doped P2-Na2/3Fe1/3Mn2/3O2 for Na-ion batteries

P2-Na2/3Fe1/3Mn2/3O2 (NFM) is a layered transition material with abundant raw materials, high specific capacity, and excellent cycling stability, a potential cathode material for sodium-ion batteries. The considerable size and substantial mass of Na+ present notable challenges concerning unfavorable reaction kinetics and structural instability during the insertion and extraction processes. This presents a formidable obstacle for practical applications. Ta5+ is characterized by higher valence and more muscular bonding energy, and doping Ta in NFM leads to the formation of a stable crystal structure. In the present work, we use first-principles calculations within the DFT + U framework to investigate different concentrations of Ta-doped MFMs to overcome these drawbacks. The calculated results show that the introduction of Ta elements reduces the formation energy and enhances the structural stability. It also enhances the electronic conductivity (i.e., the band gap, Eg = 0) and lowers the ion mobility barrier. In addition, we also investigate the electronic structure, spin, and magnetic properties of doping controlled electrode materials to investigate the doping effect regulating migration energy barriers. This study suggests that Ta-doped NFMT is a good alternative due to higher performance compared to the pristine NFM.

K/Zn dual-site doping toward ultralow-strain P2-type Ni/Mn-based cathode materials for sodium-ion batteries

Charging P2-type Na0.66Ni0.33Mn0.67O2 (NNM) to a high upper cut-off voltage of 4.3 V (vs. Na+/Na) can yield a competitive discharge voltage (3.6 V-class) and capacity. However, achieving stable cycling for NNM under this condition remains challenging owing to an unfavorable phase transition and a large lattice-volume change. Herein, a dual-site doping strategy is used to simultaneously realize a pinning effect at the Na and transition metal sites. Incorporating pinned K+ and Zn2+ ions considerably enhances the structural stability of NNM, affording a complete single-phase reaction with ultralow strain (only 0.54 % variation in volume) during Na+ insertion/extraction. The synergistic contributions of dual-site doping to the enhanced electronic conductivity, lowered Na+ migration barrier, and increased Na+ diffusion coefficients are confirmed via theoretical calculations. Consequently, the K+/Zn2+ dual-site-doped Na0.63K0.03Ni0.26Zn0.07Mn0.67O2 delivers satisfactory discharge capacities of 118.6 and 63.2 mAh g−1 at 10 and 2000 mA g−1, respectively, and achieves an excellent capacity retention of 81.2 % after 200 cycles at 500 mA g−1. This study provides a promising method to strengthen the stability of the Ni − Mn-based layered framework and optimize other high-voltage and high-capacity layered oxide cathode materials.

The Distance Between Phosphate-Based Polyanionic Compounds and Their Practical Application For Sodium-Ion Batteries.

Sodium-ion batteries (SIBs) are a viable alternative to meet the requirements of future large-scale energy storage systems due to the uniform distribution and abundant sodium resources. Among the various cathode materials for SIBs, phosphate-based polyanionic compounds exhibit excellent sodium-storage properties, such as high operation voltage, remarkable structural stability, and superior safety. However, their undesirable electronic conductivities and specific capacities limit their application in large-scale energy storage systems. Herein, the development history and recent progress of phosphate-based polyanionic cathodes are first overviewed. Subsequently, the effective modification strategies of phosphate-based polyanionic cathodes are summarized toward high-performance SIBs, including surface coating, morphological control, ion doping, and electrolyte optimization. Besides, the electrochemical performance, cost, and industrialization analysis of phosphate-based polyanionic cathodes for SIBs are discussed for accelerating commercialization development. Finally, the future directions of phosphate-based polyanionic cathodes are comprehensively concluded. It is believed that this review can provide instructive insight into developing practical phosphate-based polyanionic cathodes for SIBs.

Investigation of Na7V3(P2O7)4/carbon composite as cathode material for sodium-ion battery: Influences of carbon additives and voltage windows

A sequentially processed method is developed to prepare a high-voltage cathode material sodium vanadium diphosphate Na7V3(P2O7)4 for Na-ion battery. We find that the growth of Na7V3(P2O7)4 generally introduces growth orientation due to their hybrid ionic and covalent bonding. The crystal growth of the diphosphate prefers to grow perpendicular to [002] direction, leading to an increase of the diffusion length of Na+ ion. To regulate the growth of crystal, three kinds of carbon additives, graphene oxide, Cabot carbon black and Ketjen carbon black are adopted to tune the morphologies of Na7V3(P2O7)4 to further improve its electrochemical performances. The morphologies and physicochemical properties of carbon additives and corresponding prepared Na7V3(P2O7)4 are both well characterized to clarify the effects of carbon additives on the growth process. We find that the Cabot carbon black can dramatically weaken the oriented growth direction and produce fine morphology. By adding Cabot carbon black to the sequential process, the reversible capacity of Na7V3(P2O7)4 can reach to 76 mAh g−1 with good cyclability within the voltage window of 2–4.5 V. An average voltage of 3.8 V can be obtained due to the strong inductive effect of diphosphate group.

Ti/Co co-doped O3-Na(Ni0.3Fe0.2Mn0.5)0.85Ti0.1Co0.05O2 with high rate and durable cathode material for sodium-ion batteries

O3-type layered oxides are widely investigated as cathodes for Na-ion batteries (SIBs) due to their high theoretical capacities and splendid initial Coulombic efficiency. However, they suffer from fast capacity fading owing to the complicated phase transformations, especially in high cut-off voltage (>4 V). Herein, Ti and Co elements were simultaneously introduced to O3-Na(Ni0.3Fe0.2Mn0.5)0.85Ti0.1Co0.05O2 (NFMTC) cathode material, and the effects of Ti/Co co-doping on phase structure and electrochemical properties were analyzed in detail. The results reveal that Ti/Co co-doping can enhance the {010} plane, interlayer space and Na-ion diffusion kinetics, resulting in the improved electrochemical performance. Therefore, the NFMTC cathode delivers a high reversible capacity of 174.7 mAh g−1 at 0.1 C in the voltage range of 2.0–4.3 V and a good rate capability (53% of the initial capacity at 5 C) as well as an excellent capacity retention of 78% after 300 cycles at 1 C. This work maybe provides a guidance to explore high-performance cathode materials for sodium ion batteries.

Dynamic Electrochemical Action of Low Temperature Plasma Exposed NaFePO4/Activated BCC Nanocomposites in Cathode Applications

Abstract In this research, we designed a high performance cathode materials for sodium-ion batteries derived from cold plasma exposed NaFePO4/activated bamboo charcoal (BCC). XRD, FTIR, FESEM, and Brunauer–Emmett–Teller (BET) were used to examine the crystal structure, functional groups, morphological features, and surface area of the composites. The material's surface characteristics, such as wettability, adhesion, and conductivity analysis, were proved, and the energy storage capacity of the material and these characteristics were magnified by exposure to DC glow discharge plasma. In this work, the NaFePO4/activated BCC was subjected to DC glow discharge plasma with various plasma producing gases. The electrochemical investigation shows that the air plasma-treated composite produces the best results when compared to the untreated sample. The enhancement of the diffusivity of the composite reveals that the plasma-treated materials are appropriate for energy storage devices.